Dual flush toilets are well known and allow the user the choice of effecting a large volume, "long" flush to dispose of solid waste or a smaller volume, "short" flush to dispose of liquid waste. It has previously been determined that typically the majority of flushes could be short flushes and thus a significant reduction can be obtained in the requirements for fresh water by the use of dual flush toilets. Furthermore, a corresponding reduction in the volume of sewage produced can also be obtained. These reductions offer economic benefits to those households with metered water usage, and environmental benefits by reducing fresh water usage by a toilet and the volume of sewage produced by the toilet which must be treated.
An example of a prior art dual flush toilet is shown in U.S. Pat. No. 4,225,987 to Goldman et al. This reference shows a dual flush mechanism which requires a modified ball valve and a complex vent control means to be installed in the toilet tank. The ball valve in this reference includes a vented outlet to release the air from the ball to eliminate the valve's buoyancy. The vent control means is attached to two flush handles each of which corresponds to a particular length flush and has an associated float control arm. When either handle is depressed, the valve is opened and water leaves the tank until the float control arm corresponding to the pressed handle drops as the water exiting the toilet tank drops below its float. When the float control arm drops, the air is vented from the ball and the valve closes. The handle which provides a long flush accordingly has a long float control arm and the handle which provides a short flush has a shorter float control arm.
Another example of a prior art dual flush toilet is shown in U.S. Pat. No. 4,864,665 to Toltzman. This reference teaches a dual flush mechanism with two flush handles. Operation of one of the flush handles, corresponding to a long flush, results in the ball valve being lifted to its buoyant position and the toilet flushes in the normal manner. Operation of the flush handle corresponding to a short flush, results in the ball valve being lifted just off of its seat so that the ball valve is subject to the venturi effect, or suction, generated by the water flowing out of the tank through the valve seat. The ball valve remains open only so long as the user maintains the short flush handle in its depressed position which keeps the ball valve in its open position. Thus, the user of the toilet is required to maintain the short flush handle in the depressed position just long enough to ensure disposal of the liquid waste in the toilet bowl and then to release the handle to allow the ball valve to close, terminating the flush.
Another prior art example of a dual flush toilet is shown in U.S. Pat. No. 4,764,995 to Harney. This reference shows a mechanism similar in concept to that shown in the above-mentioned Toltzman reference except the duration of the short flush is controlled by a control float which actuates a rack and pinion arrangement. When a short flush is selected, the rack operates to maintain the ball valve in a slightly opened position until the control float drops to a predefined level. Thus, there is no need for the user to maintain the handle in the depressed position as the flush will terminate automatically.
While many different prior art dual flush systems exist, they each have problems and disadvantages associated with them. Some prior art systems, like the Toltzman system, require the operator to control manually the duration of the short flush. Other prior art systems, like the Goldman et al. reference, require a substantial modification of the toilet tank hardware, such as a replacement of the main valve and seat. Still other prior art systems, like the Harney reference, require a control mechanism which is complex, and therefore expensive to manufacture, and which may be difficult to install and adjust in existing toilet systems.